1. Field of the Invention
The present invention relates to printing machines having at least one machine element that can be adjusted using a setting element, to affect a quality of a printing performed by the printing machine, wherein an optical detection device having a sensor that is directed toward a surface of a printing substrate printed in the printing machine detects the quality of the printing during the transport of the printing substrate through the printing machine, and wherein a control device that receives data from the optical detection device uses the setting element to adjust the at least one machine element based upon a difference between a quality of the printing that is preset as the target value and the quality of the printing that is detected by the optical detection device as the actual value, in a manner that serves to minimize the difference between the target value and the actual value.
2. Description of the Background Art
EP 0 763 426 B1 and DE 195 33 822 A1, which establishes the priority of the former publication, disclose a method for controlling inking in printing with a printing machine, especially a sheet-fed offset printing machine comprising multiple printing couples in which, for example, an imaging device is used to obtain actual colorimetric values for a multitude of selected measuring points distributed over the entire surface of an image substrate. These values are stored as reference values for at least one subsequent printing, wherein in the subsequent printing actual values are obtained at measuring points that coincide with the previously selected measuring points, wherein the inking in the print run is controlled only at those measuring points that change the most, by means of setting elements that act upon said measuring points. Elements for setting the coating thickness of the printing ink, for setting the quantity of dampening agent, and for setting the register, all of which are active in zones, are listed as setting elements. A control unit that controls the respective setting elements and an imaging device that scans the entire printed surface of a sheet are provided. Inputs into a data processing unit that is connected to the control unit can be accomplished via a keyboard.
EP 0 598 490 A1 discloses a color register system for a printing machine, wherein a computer uses a camera or a group of cameras to detect any misalignment of colors in a printed image by comparing a relevant image with a stored reference image, and uses a print controller to align a longitudinal, transverse and rotational position of cylinders in the printing machine relative to a web that is passed through the printing machine for printing, such that said cylinders will generate a multi-color image with colors that are aligned properly relative to one another.
EP 0 882 588 A1 discloses a device and a method for the register-true coordination of printing cylinders in a web-fed rotary printing machine, wherein a first cylinder that prints on one side of the web is actuated by a first motor and a second cylinder that prints on the same side of the web is actuated by a second motor. The angular position of the second cylinder is coordinated with the first cylinder via a controller to be register-true, wherein register marks printed on the web by the cylinders are scanned by a sensor, such as a CCD camera, which is positioned downstream from the last cylinder in the direction of production, and are evaluated for the controller using identifying characteristics as reference variables.
DE 197 36 339 A1 discloses a printing machine with impression cylinders designed for printing on a substrate and having an inking unit that comprises an ink fountain and is assigned to a forme cylinder, wherein temperature-control elements are allocated to at least one inking roller and preferably also to the forme cylinder. The temperature-control elements are equipped with a controlling or regulating device, in which, using preset values, reference temperature values for the printing ink can be adjusted for at least one inking roller, wherein the preset values can be based upon an optical density measured on the substrate using a photometric sensor or a densimeter, such as is customarily used in the printing industry, and can thus be derived especially from a printed image evaluation of printed samples drawn from a print run.
DE 102 18 359 A1 discloses a web-fed rotary printing machine comprising one printing couple with which printing ink can be applied to a substrate that passes through the printing couple, wherein a least one component that operates in conjunction with the printing ink and can be controlled via a temperature-control device is provided, wherein the tack of the printed ink in a specific area can be adjusted by said temperature-control device.
EP 1 512 531 A1, which was published subsequent to the priority date of the subject application, discloses a method and a device for controlling inking in a printing machine, wherein a color recognition device comprising a multitude of color sensors stationarily attached to the printing machine is provided for the whole-surface optical scanning of the entire width of the printed product in which one rapid primary color-measuring signal is scanned per color zone. Integration is performed along the print direction, over a color image range for the printed product that can be preset, wherein the total actual surface coverage is calculated for at least one printing ink, wherein a comparison with a reference surface coverage is made, and wherein a color correction signal is generated for the color zone and the printing ink.
WO 2005/016806 A1, which was published subsequent to the priority date of the subject application, discloses a method for regulating the cut-off register of a web-fed rotary printing machine, in which specific image data or measurement marks on printed webs are recorded by sensors and supplied to a regulating device. Before and/or on the common cutting cylinder, image information or a measurement mark from at least one of the printed webs that is applicable to the deviation in the position of the printed image relative to its reference position based upon the location and the time of the cut, in other words applicable to the cut-off register error, is recorded, evaluated and/or converted to an actual value with the help of at least one sensor. This actual value serves in regulating the cut-off register error of at least one web, and that for the correction of the cut-off register error of the at least one web either the speed of at least one clamping point that lies in front of the cutting cylinder and/or the position of the cutting cylinder is changed, so that the cut-off register error of the at least one web is corrected to a preset reference value on the basis of the actual value.
U.S. Pat. No. 6,796,227 B1, which was published subsequent to the priority date of the subject application, discloses a printing machine with multiple sequentially arranged printing couples, wherein a dampening unit is allocated to each of the printing couples. Each dampening unit dampens one printing forme that is arranged on a forme cylinder of the printing couples, in multiple zones in longitudinal rows along the forme cylinder, wherein in each of the zones a control device with a camera measures a color density of the printing ink that is applied to a printing substrate in the printing machine. The control device adjusts a metering of the dampening agent in the zones with the help of a correction signal that is derived from the measurement of the color density.
U.S. Pat. No. 6,796,240 B2, which was published subsequent to the priority date of the subject application, discloses a printing machine with multiple sequentially arranged printing couples, wherein the printing couples print different color patches of the same printed image, a control device uses a camera to scan a color-measuring bar applied to a printing substrate and the control device controls both a color register and a color density.
U.S. Pat. No. 6,782,814 B2, which was published subsequent to the priority date of the subject application, discloses a method and a device for detecting register errors and an automatic register control for a multicolor rotary printing machine, wherein register marks printed onto a paper web are scanned using a CCD camera, and the centers of gravity of the register marks are evaluated in comparison with a reference position.
The known devices for influencing a quality of printing essentially follow a singular approach to a solution, in that they view an individual interfering factor separately from its interaction with another interfering factor having a different cause. This does not adequately address what actually occurs in practice.
Clients ordering printed products are placing ever increasing demands on the quality of printed products created using printing machines, wherein the concept of the quality of a printing, through properties shown in samples of the printing, forms a complex level. This level is most frequently characterized by a multitude of parameters, which are to be achieved and maintained for all the copies of the printed product, to the greatest possible extent, by the party creating the printed product with the printing machine, optionally taking into account an agreed-upon permissible margin of error. Thus for financial reasons alone, it is necessary for the party performing the printing to minimize wasted paper from non-salable copies of the printing, both in the final proof and in the print run.
In the print run even high-precision machine elements of the printing machine are subject, for example, to changes caused by wear and tear, and even high-quality materials processed in the print run are subject, for example, to thermal changes. Thus, the structural dimensions of printing machines for the most part cannot alone guarantee a reproducibility of the copies that make up the printing. As a result, technical measures that constitute a component of the printing process are also necessary in order to ensure that the quality of the printed product promised to the client ordering the printing, and thereby the properties that define said quality, can be achieved and consistently maintained. These properties relate especially, for example, to the inking of the printed product, the scope of the tonal values reproduced in the printing, the sharpness and the contrast of printed halftone dots, the precision of the overprinting of color patches involved in the printing and belonging to a specific printed image, and the positioning accuracy of printed images printed on both sides of a printing substrate.
Each of these properties can be influenced in a sustained manner, alone or in combination, among other things by the properties of the materials used in the printing, for example the printing ink and/or the printing substrate, by their behavior as they are transported through the printing machine, and by the setting of machine elements involved in the printing and/or the temporal response to a change in their setting, in other words the time required to reach an operating state that is stable with respect to the printing process following a change in the setting of one or more machine elements. This approach results in a complex control system for the printing machine, in which the quality of the printing is viewed as a controlled process that inhibits interfering factors and must be regulated.